1. Field of the Invention
The present invention relates generally to wavelength division multiplexing/demultiplexing, and more specifically, a mounting for a diffraction grating.
2. Description of the Related Art
The telecommunications industry has grown significantly in recent years due to developments in technology, including the Internet, e-mail, cellular telephones, and fax machines. These technologies have become affordable to the average consumer such that the volume of traffic on telecommunications networks has grown significantly. Furthermore, as the Internet has evolved, more sophisticated applications have increased data volume being communicated across the telecommunications networks.
To accommodate the increased data volume, the infrastructure of the telecommunications networks has been evolving to increase the bandwidth of the telecommunications networks. Fiber optic networks that carry wavelength division multiplexed optical signals provide for significantly increased data channels for the high volume of traffic. An important component of the fiber optic networks is a wavelength division muitiplexer/demultiplexer (WDM). The WDM is utilized to multiplex and/or demultiplex the wavelength division multiplexed optical signals in the fiber optic networks.
The WDM includes optical components that, in the case of demultiplexing, separate polychromatic optical signals into monochromatic or narrowband optical signals, and, in the case of multiplexing, combine monochromatic optical signals into polychromatic signals. The optical components of the WDM generally include lenses for focusing and collimating the optical signals and a diffraction grating for diffracting the optical signals to perform the multiplexing and demultiplexing functions. A diffraction grating component generally comprises an elastomer material, such as epoxy, on which the diffraction grating profile is pressed; an optical reflective coating, such as gold or aluminum, that is coated onto the elastomer; and a substrate on which the elastomer material is attached. The substrate provides thermal stability to maintain groove spacing over the operating temperature of the diffraction grating.
A support structure is used to either mount or house the optical components of the WDM. To maintain optical fidelity of the WDM, the diffraction grating should be aligned and maintained at a particular position from the last optical component prior to the diffraction grating. Maintaining the diffraction grating at the particular position, however, is non-trivial due to thermal characteristics of the support structure. Based on the coefficient of thermal expansion (CTE) of the material of the support structure, conventional support structures may undesirably change size over a temperature range that extends from xe2x88x9240C to +85C, thereby causing an undesirable change of position of the diffraction grating.
To overcome the problem of maintaining a particular position of a diffraction grating in relation to a last optical component prior to the diffraction grating in a wavelength division multiplexer (WDM), the diffraction grating is thermally isolated from a support structure that supports the other optical components of the WDM. The diffraction grating may be thermally isolated from the support structure by utilizing pins that couple the support structure and the diffraction grating. The pins may be thermally matched to the support structure of the WDM.
One embodiment of the WDM includes a support structure that is coupled to the at least one optical component. A diffraction grating is optically coupled to at least one optical component coupled to the support structure. A frame supports the diffraction grating. Pins are coupled between the support structure and the frame so as to substantially thermally isolate the frame from the support structure. The pins may be substantially geometrically equally spaced along the support structure and have approximately the same exposed length extending from the support structure. The pins may have the same coefficient of thermal expansion as the coefficient of thermal expansion of the support structure.